The invention relates to a device for the transcutaneous administration of substances by means of iontophoresis.
Transcutaneous iontophoresis is a known technique for administering substances to the body through the skin in localised fashion and with minimum haematic absorption of the substances, reducing the risk of side effects linked to their uncontrolled diffusion. Some substances which can be administered may be, by way of example, drugs, herbal remedies, cosmetic and homeopathic products. Transcutaneous iontophoresis is used, for instance, in aesthetic medicine (for instance in the treatment of cutaneous tissue blemishes) or in pain relieving, relaxing or tonicising therapies.
Transcutaneous iontophoresis consists of letting an electrical current pass between a selected portion of skin and an electrode through a transport fluid interposed between the skin and the electrode and in which are dissolved or dispersed the molecules of the substance to be administered (usually in ionic, or electrolytic, or otherwise electrically charged form). The electrical circuit is closed applying one or more counter-electrodes on different parts of the skin from the treated one. The electrical current is applied according to an appropriate time-based wave form which allows to transfer the substances at a predetermined depth into the skin and based on predetermined mean square values over time.
The transport fluid is usually in the form of a gel.
Appropriate devices are constructed to apply this technique.
In particular, known devices for the transcutaneous administration of substances by means of iontophoresis comprise a hollow operative head made of plastic material, provided with two openings on two opposite sides. An opening, into which is inserted a container of the fluid, acts as an inlet for the fluid. The other opening is closed to measure, except for a minimum space along the long edges, by a plastic roller, free to rotate about its own axis and acting as a dispenser of the transport fluid. The part of the roller inside the cavity is in contact with the fluid coming from the container and it rotates, by effect of friction with the skin, when the roller is applied to the skin with the device kept in motion. The roller thereby brings the part covered with fluid in contact with the skin, distributing the fluid. To continue dispensing the fluid, the roller must thus be maintained in continuous rotation. A thin lamina folded in the shape of an “L” is inserted into the chamber as an electrode. The short side of the lamina is fastened to the wall of the operative head and it bears an electrical terminal external to the head, connected with a voltage driven current generator (which, in turn, is connected to one or more counter-electrodes). The long side of the lamina faces the roller along the axis of rotation with a plane of lay converging on the axis itself and practically nearly in contact therewith. The electrode thus applies voltage at a very short distance from the surface of the roller and the current, to reach the skin, must travel through the whole circumference of a section of the roller within the very thin layer of fluid adhering to its surface. Given the characteristics of the fluid, the electrical impedance of this segment is usually high. Furthermore, it is highly variable and its value cannot be reliably controlled. The thickness of the fluid layer distributed on the cylinder in the outer part is variable over time according to the conditions of the skin, of the pressure exerted thereon by the roller, of the deformation of the operative head due to the pressure of the operator's fingers, which alters the geometry of the long sides of the aperture whereto the roller is applied. Moreover, when the skin is already moistened by the fluid, friction on the skin may not be sufficient to cause the roller to rotate (unless a strong pressure is exerted on the skin, which can be annoying for the patient). The roller thus dries up, stopping its distribution of fluid, and the electrical impedance imposed on the generator increases. Additionally, the lamina, which is fastened only on one side and very thin, can tend to deform elastically. The device is voltage driven and it maintains a given current (according to a certain waveform). Therefore, impedance variations may give rise to voltage fluctuations and peaks which can cause discomfort and even small burns to the patient. Moreover, the plastic roller is easily scratched and deteriorates, diminishing its ability to rotate and drive the fluid and becoming difficult to clean. In addition, it cannot be easily sterilised.